Dehydroisomerization process

ABSTRACT

ALKYLCYCLOPENTANES AND GASOLINE OR NAPTHA FRACTIONS CONTAINING THE SAME ARE DEHYDROISOMERIZED TO AROMATIC COMPOUNDS BY CONTACTING WITH A FLUORIDED GROUP VII-B OR VIII METAL-ALUMINA CATALYST AND A CARBON OXIDE AS A CONVERSION REACTION MODERATOR. BY EMPLOYING A FLUORIDED METAL-ALUMINA CATALYST AND A CARBON OXIDE MODERATOR, SUCH AS CARBON MONOXIDE OR CARBON DIOXIDE, ALKYLCYCLOPENTANES ARE SELECTIVELY CONVERTED TO AROMATICS AND GASOLINE OR NAPTHA FRACTIONS CONTAINING THE SAME ARE UPGRADED.

United States Patent 3,756,941 DEHYDROISOMERIZATION PROCESS Norman D. Carter, Poughkeepsie, John H. Estes, Wappingers Falls, and Stanley Kravitz, Wiccopee, N.Y., assignors to Texaco Inc., New York, N.Y. No Drawing. Filed June 21, 1971, Ser. No. 155,348 Int. Cl. Cg 35/06, 35/08 US. Cl. 208-135 18 Claims ABSTRACT OF THE DISCLOSURE Alkylcyclopentanes and gasoline or naphtha fractions containing the-same are dehydroisomerized to aromatic compounds by contacting with a fluorided Group VII-B or VI II metal-alumina catalyst and a carbon oxide as a conversion reaction moderator. By employing a fluorided metal-alumina catalyst and a carbon oxide moderator, such as carbon monoxide or carbon dioxide, alkylcyclo pentanes are selectively converted to aromatics and gasoline or naphtha fractions containing the same are upgraded.

BACKGROUND OF THE INVENTION This invention relates to the production of aromatic hydrocarbons from naphthenes and from petroleum fraction containing naphthenes. In particular, this invention relates to a process for effecting dehydroisomerization of five memberednaphthene ring hydrocarbons to aromatics such as the conversion of methylcyclopentane to benzene.

Alkylcyclopentanes are found as components of light straight run gasoline and are contained in other gasoline fractions such as naphtha fractions resulting from thermal and catalytic conversion of petroleum. Typically, saturated gasoline or naphtha fractions are treated or up graded to improve their anti-knock characteristics. One means of upgrading such streams is by the Well known process of reforming wherein naphthetic hydrocarbons such as cyclohexane compounds are dehydrogenated to aromatics. However, subjecting five memb'ered naphthene ring compounds such as alkylcyclopentanes to conventional dehydrogenation or reforming catalysts and processing conditions causes the formation of minor amounts of cyclic mono-olefins and di-olefins in addition to the production of undesirable amounts of carbonaceous deposits on the catalyst in view of the naphthenes susceptibility to cracking. While some isomerization of alkylcyclopentanes to cyclohexanes may occur, the overall effect has been to downgrade such components to less valuable products having little or no value as gasoline blending components. Likewise, the practice of separating five membered naphthene ring hydrocarbons to separately isomerize such compounds to cyclohexanes followed by dehydrogenation of the cyclohexanes to aromatics is at best a poorly selective process involving the use of a plurality of catalysts and reaction zones which from a processingstandpoint remains economically unattractive.

It is therefore an object of this invention to provide a process for converting alkylcyclopentanes and fractions containing the same to aromatic compounds.

Another object of this invention is to provide a means for upgrading gasoline and naphtha fractions containing alkylcyclopentanes.

Another object of this invention is the direct production of benzene from methylcyclopentane.

Yet another object of this invention is to provide a means for converting alkylcyclopentanes to aromatics by 3,756,941 Patented Sept. 4, 1973 Fee employing a catalyst having hydrocracking and hydrogenation activity under processing conditions capable of controlling catalyst activity and selectivity.

Other objects and advantages will become apparent from a reading of the following description and examples.

SUMMARY OF THE INVENTION Broadly, this invention contemplates a process for the dehydroisomerization of al-kylcyclopentanes to aromatic hydrocarbons which comprises contacting a hydrocarbon charge stock containing alkylcyclopentane with a fluorided Group VIIB or VII metal-alumina cataylst in the presence of hydrogen and a carbon oxide wherein the carbon oxide is introduced to said process at the rate of from about 5 10- to 5X10 gram mole of carbon oxide per hour per gram of said catalyst. Carbon oxides contemplated herein and introduced in the course of the process include carbon monoxide and carbon dioxide and preferably carbon monoxide.

In accordance with the present invention We have found a means for reversibly controlling the selectivity of an alkylcyclopentane dehydroisomerization process through the addition of a carbon oxide as a moderator during the period of reaction. The beneficial effect hereinafter more fully described was unexpected inasmuch as carbon oxides such as carbon monoxide have heretofore been known as catalyst poisons and especially strong deactivators of Group VIII metal catalysts. In particular, carbon oxide' introduction provides a means for altering catalyst selectivity and the course of the dehydroisomerization reaction. Most importantly, the course of the reaction and selectivity are not only controllable but reversible. Significantly, the presence of carbon oxide process moderator permits a fine tuning of the catalytic system to optimize a particular set of products from a complex reaction.

According to our invention, dehydroisomerization of alkylcyclopentanes is conducted in a single or continuous reaction stage wherein high conversion of the naphthene is undertaken providing high yields of recoverable liquid product including improved selectivity toward aromatic compounds. The dehydroisomerization process described herein is conducted in the presence of a fluorided Group VII-B or VIII metal-alumina catalyst under conversion conditions including temperatures of from about 750 to 1000 F., preferably 850 to 950 F., hydrogen to hydrocarbon mole ratios in the range of about 0.1:1 to 12:1, preferably 0.5:1 to 8:1 and when conducted as a continuous reaction at liquid hourly space velocities of from about 0.5 to 8, preferably 1 to 4.

As mentioned above the process employs a catalyst comprising a member of Group VII-B or VIII of the Periodic Table, alumina and fluorine and represents a well known class of hydrocracking or reforming catalyst. Exemplary of the Gorup VII-B and VIII metals forming a component of the catalyst we mention rhenium, platinum, palladium, rhodium and ruthenium, where the metal or combinations thereof is present in an amount of from about 0.01 to 5.0 weight percent and preferably from about 0.1 to 2.0 weight percent based on the composite catalyst. Aluminas in various forms may be used as a component of the catalyst and particularlythose aluminas having replaceable surface hydroxyl groups and surface areas of from S0 to 800 square meters per gram using the BET method. Included with our definition of alumina, we mention for example eta-alumina, gammaalumina, silica-stabilized alumina, i.e., aluminas containing approximately 5 weight percent silica, thoria-alumina,

zirconia-alumina and titania-alurnina. Preferably, we em ploy aluminas having surface areas of from 50 to 400 square meters per gram and particularly etaand gammaalumina. Further, the catalyst is provided with additional acidity by virtue of the presence of from about 0.5 to 15.0 weight percent chemically combined fluorine and preferably from 0.5 to 6.0 weight percent.

Pursuant to our invention, the role of our carbon oxide moderator, such as carbon monoxide, in the dehydroisomerization of alkylcyclopentanes and alkylcyclopentane fractions in contact with the aforementioned catalyst and hydrogen is to suppress the cracking aspect of the catalyst by which We mean to interfere with the acidity function of the catalyst surface while at the same time avoiding permanent damage or poisoning of the catalyst. In this regard, we have found that low concentrations of the moderator introduced in the course of converting the naphthene to an aromatic strongly shifts the product distribution such that the catalyst is moderated to the extent that the cracking propensity of the catalytic material is inhibited. Consequently, the nature of the conversion reaction can be converted from one producing substantial quantities of hydrocracked gaseous products, olefinic materials and hydrocarbonaceous deposits to a highly selective process wherein alkylcyclopentanes are converted to aromatics in conjunction with high liquid recoveries. Discontinuation of carbon oxide introduction to the process results in a reversal of catalyst selectivity and lower conversion to recoverable liquid products and redirects the reaction towards the original conditions, that is to say substantial cracking of the feedstock will again occur. As can be seen the effect of moderator addition is reversible, i.e., diminished or eliminated rates of moderator addition reverse the process from one dehydroisomerization towards hydrocracking.

Low concentrations of carbon oxide introduction during the course of conversion have been found to perform the function detailed above. The amount of moderator beneficially employed and introduced in the course of the process varies from about 10 to 5 X gram mole of moderator per hour per gram of catalyst and preferably from about 1 l0- to 2.5 x10" gram mole of moderator per hour per gram of said catalyst. The preferred carbon oxide moderator employed in our process is cabon monoxide.

In selecting the amount of moderator introduced during conversion we have found that the rate of carbon oxide introduction is dependent upon the temperature of the reaction such that higher amounts of moderator are required to inhibit cracking at higher temperatures while lesser amounts perform the same function at lower temperatures. Amounts such as 7 10- to 1.3 l0 gram mole of moderator per hour per gram of catalyst are suflrcient where the process is carried out at temperatures of about 850 F. whereas higher amounts such as 1.3 10 to 2.3 l0- are needed when processing temperatures are about 925 F. Likewise, carbon oxide introduction and its effect upon the process is responsive to the percent fluorine on the catalyst. A catalyst containing lower amounts of fluorine such as 0.5 weight percent requires less carbon oxide to moderate the reaction, whereas fiuorine contents of about 6 weight percent require the higher rates of carbon oxide introduction. One convenient means of introducing the moderator to the reaction zone is to add the moderator to the hydrogen stream prior to hydrogen introduction to the reaction chamber. Moderator introduction can be on a continuous basis or alternatively, the carbon oxide may be pulsed or intermittently introduced to the reaction such that the rate of carbon oxide introduction is within the ranges stated above.

By providing a means for controlling the activity and selectivity of the process conducted in the presence of the aforementioned catalyst through the use of a carbon oxide moderator a plurality of alkylcyclopentanes alone or in admixture and fractions containing the same are readily selectively dehydroisomerized to more valuable aromatic products. For example, C to C alkylcyclopentanes including for example methylcyclopentane and l,Z-dimethylcyclopentane, alone or in raflinate fractions can be dehydroisomerized in the presence of the catalyst, moderator and conversion conditions recited above to benzene, toluene and xylenes, The conversion is accomplished with minimal cracking such that liquid recoveries of and higher are easily obtained. In a highly preferred embodiment, methylcyclopentane is selectively converted to benzene. In a similar manner, petroleum fractions such as light straight run gasoline having an initial boiling point of about 70 F. and an end point of about 400 F. containing C to C alkylcyclopentanes are converted under the conditions recited above such that substantial conversion of the alkylcyclopentanes to high octane aromatics such as benzene, toluene and isomeric xylenes occur.

In order to illustrate more fully the nature of our invention and manner of practicing the same the following examples are presented. In these examples the best mode contemplated by us for carrying out our invention is set forth.

A charge stock comprising commercial methylcyclopentane was contacted with a catalyst comprising 0.5 weight percent platinum on alumina fluorided to a 1 percent level. Conversion conditions included reaction temperatures of 800 F. and 850 F., 300 p.s.i.g. of hydrogen flowing at the rate of three cubic feet per hour, a catalyst charge of 85 grams cc.) and the charge stock was introduced at the rate of 100 cc. per hour or a space velocity of 1.0. Analysis of the charge stock showed it to contain the following; methylcyclopentane 80.3 percent, hexanes 11.8 percent, benzene 4.6 percent and cyclohexane 3.3 percent. Initial conversion was undertaken at temperatures of 800 F. and 850 F. to establish the activity and selectivity of the catalyst and process in the absence of a carbon oxide moderator. Samples were collected after each four hour processing period and analyzed by gas chromatography. Table I summarizes the results for the conversion periods.

TABLE I Period 1 2 Time, hours 4 4 Temperature, F 800 850 Moderator introduction..- None None 88. 0 (i8. 5

40.4 16.1 6. 57.0 Cyclohexane 11.5 2.9 Hermes 42.0 24.0 Benzene yield, percent of charge 5.4 38.8

As seen from Table I, benzene yields are governed by the rate of conversion of methylcyclopentane and the loss of naphthenes to side cracking reaction. Increasing the reaction temperature from 800 F. to 850 F. significantly reduced the amount of recoverable liquid product at increased conversion rates. The benzene yield, that is the amount of benzene basis the total feed, increased with the higher severity to 38.8%. However, the loss in liquid product of about 20 percent due to cracking became a limiting factor in the attainable benzene yield.

Additional conversion of the feedstock was undertaken employing the aforementioned conditions at a temperature of 850 F. in the presence of carbon monoxide introduced at the rate of 9.2 10- gram mole per hour per gram of catalyst during periods 3 to 5. Conversion was continued during periods 6 to 8 in the absence of further moderator addition and Table II summarizes the results.

From Table II, the introduction of the moderator carbon monoxide suppresses the cracking activity of the catalyst as seen from the increased liquid recovery and significantly improves the yield of benzene. At the above conditions there is a general increase in liquid recovery of up to 91.5 percent. Based on the total feed to the unit about 50 percent is converted into benzene. By ceasing carbon monoxide introduction in periods 6 to 8 cracking activity increases with increased gas production and a gradual loss in benzene yield.

Example II A charge stock comprising commercial methylcyclopentane mixed with normal heptane indicated on analysis to contain the following: methylcyclopentane 40.1 percent, hexanes 5.9 percent, benzene 2.3 percent, cyclohexane 1.7 percent and normal heptane 50.0 percent. The charge stock was contacted with a catalyst comprising 0.5 weight percent platinum on alumina fluorided to a one percent level. Conversion conditions included reaction temperatures of 850 F., 900 F. and 950 F., 250 p.s.i.g. of hydrogen flowing at the rate of 3 cubic feet per hour, a catalyst charge of 100 cc. and the charge stock was introduced at the rate of 100 cc. per hour on a space velocity of 1.0. Initial conversion was undertaken at 850 F. to establish the activity and selectivity of the catalyst and process in the absence of a carbon oxide moderator. Samples were collected after each four hour processing period and analyzed by gas chromatography. Table III periods 4 and 5 gave higher yields than period 1 and the overall product likewise contained more aromatics. Specifically in period 5, the liquid yield was brought up to 47.9 percent and the aromatic content was 70 percent.

We claimf. V I

1. A process .for the dehydroisomerization of alkylcyclopentanes to aromatic'hydrocarbons which comprises contacting a hydrocarbon charge stock containing alkylcyclopentane with a fluorided Group VII-B or VIII metalalumina catalyst wherein said catalyst comprises from about 0.01 to 5.0 weight percent of a metal selected from the group consisting of platinum, palladium, rhodium, ruthenium and rhenium in the presence of substantially pure hydrogen and a carbon oxide, wherein said carbon oxide is introduced to said process at the rate of from about 5 X 10* to 5 X 10- gram mole of carbon oxide per hour per gram of said catalyst.

2. A process according to claim 1 wherein said contacting is conducted at a temperature of from 750 to 1000 F.

3. A process according to claim 1 wherein said contacting is conducted at temperature of from 850 to 950 F.

4. A process according to claim 1 wherein said carbon oxide is introduced at the rate of from about 1 10- to 2.5 x 10- gram mole of carbon oxide per hour per gram of said catalyst.

5. A process according to claim 1 wherein said carbon oxide is carbon monoxide.

6. A process according to claim 1 wherein said carbon oxide is carbon dioxide.

7. A process according to claim 1 wherein said contacting is conducted at a liquid hourly space velocity of from 0.5 to 8.0.

8. A process according to claim 1 wherein said contacting is conducted at a hydrogen pressure of from 200 to 750 p.s.i.g.

9. A process according to claim 1 wherein said catalyst comprises from about 0.5 to 15.0 weight percent fluorine.

10. A process according to claim 1 wherein said catalyst comprises from about 0.5 to 6.0 weight percent fluorine.

11. A process according to claim 1 wherein said Group summanzes the results for the conversion periods. VIII metal 18 platinum.

TABLE III Period 1 2 3 4 5 Time, hours 4 4 4 4 4 Temperature, F 850 850 900 950 950 Moderator, gm. mol/hr ataly 0 5. 1X10- 5. 1X10 8. 3X10 9. 2X10 Percent liquid recovery 31. 0 76. 0 52. 7 46. 8 9 Liquid recovery analysis, wt. percent:

0, (propane 1.4 1.0 0.9 1.0 1.2 O; (butanes) 8.0 4.6 5.9 6.2 7. 2 Ca (pentanes).-- 5. 5 2. 7 5.4 5. 8 7. 2 20. 8 13.3 10. 7 10.9 7.1 4. 9 30. 2 8.4 8. 9 3. 6 10. 1 9. 5 6. 7 3. 6 2. 7 39. 0 34. 3 50. 6 52. 5 55. 7 8. 1 3. 9 8. 6 8. 2 10. 2 1.8 0. 3 1.9 2. 2 4. 1 0.5 0.8 0.8 1.0 12. 4 26. 0 26. 7 25. 0 26. 7 15. 6 29. 3 32. 2 30. 0 33. 5

From Table III, it will be appreciated that the introduction of a carbon oxide moderator, in this instance carbon dioxide, into the charge stream rapidly affected liquid yield. The moderator was introduced as a carbon dioxidehydrogen gas mixture containing four percent carbon dioxide which was metered into the hydrogen stream. Periods 2 and 3 show the efiect of introducing the moderator and thereafter raising the severity of the reaction. An increase in liquid product from 31.0 weight percent to 76.0 weight percent through periods 1 and 2 was observed resulting in almost double the yield of aromatic product. The severity increase to 900 F. in period 3 also gave higher yields than period 1 and the overall product contained more aromatics. Further increases in severity to 12. A process according to claim 1 wherein said contacting includes a hydrogen to hydrocarbon mole ratio of about 0.1:1 to 12:1.

13. A process according to claim 1 wherein said hydrocarbon charge stock is a gasoline fraction including alkylcyclopentanes.

14. A process according to claim 1 wherein said hydrocarbon charge stock is a naphtha fraction containing naphthenes including alkylcyclopentanes.

15. A process according to claim 1 wherein said alkylcyclopentane has from 6 to 8 carbon atoms.

16. A process according to claim 1 wherein said alkylcyclopentane is methylcyclopentane and said aromatic hy- 950 F. coupled with increases in moderator levels in drocarbon is benzene.

17. A process according to claim 1 wherein said alkylcyclopentane is dimethylcyclopentane and said aromatic hydrocarbon is toluene.

18. A process for producing benzene which comprises contacting methylcyclopentane with a fluorided Group VII-B or-VIII metal-alumina catalyst wherein said catalyst comprises from about 0.01 to 5.0 weight percent of a metal selected from the group consisting of platinum, palladium, rhodium, ruthenium and rhenium in the presence of substantially pure hydrogen and a carbon oxide, wherein said carbon oxide is introduced to said process of the rate of from about 5 10 to 5 X 10- gram mole of carbon oxide per hour per gram of said catalyst.

References Cited UNITED STATES PATENTS 10 HERBERT LEVINE, Primary Examiner US. Cl. X.R.

$222530 4 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,756,941 Dated Sgtember 4', 1973 Inventofla) Norman D. Carter, John H. Estes & Stanley Kravitz It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

$01. 2, line 12 "VII" should read --VIII- Col. 4, between Insert -Example I-- lines 24 and 25 C01. 4, TABLE I "6." should read --6.l--

line 53 C01. 5, TABLE III "Cyclo C should read Cyclo C lipe 54 I 6 Signed and sealed this 7th day of May 19%;.

(SEAL) Attest:

EDWARD PLFLETCHEIQJH. I C. MARSHALL DANN Attesting Officer Commissioner of Patents 7 

